A selector of this kind is described in the specification of published European patent application No. EP 0 367 668A, in which the actuator is a voltage responsive generator which is a "mirror image" of the above mentioned voltage generator, together with an electric motor which is powered through differential amplifiers of limited or fixed gain and mounted in opposition to each other. In addition, in the event of damage to the control line, the movable member assumes a predetermined position.
The selector or switching unit includes a switching member in the form of a conductive cursor for making electrical contact between one of the contact points (or electrical contact strips) and the control output terminal; the voltage generator for emitting voltages at a plurality of discrete values consists of a voltage splitting bridge with resistors.
This requires certain precautions to be taken. Thus, it is necessary for the cursor, while passing from one stable position to another, to overlie the contact strips unless this would produce, at the control output terminal, a signal equivalent to a fault in the control line, in which case the headlamp is automatically returned to its dipped position.
In addition, when two contact strips are connected to the supply inputs, it is necessary to prevent the cursor from overlying three contact strips at the same time when passing from one position to another. Accordingly, having regard to the mounting mentioned above, of the actuator (or positioning unit), the electric motor of the latter would oscillate. It is also desirable for standardization reasons to avoid having to modify the actuator, which is overall a more costly component than the selector.